Tdengine biweekly selection of community issues | phase III

Hi, Hello everyone , To prevent too many common problems from bothering users , Easy for users to learn 、 Absorb experience , We will select the common problems encountered by users in the community recently 、 Summary , Share with you in the form of a column . This is the third issue of this column , The content shared is as follows ：

Content preview

• Why do I write data in batches , Timestamp use  NOW  Function splicing will result in data loss ？

• How to smoothly expand the capacity of a cluster ？

• After cluster expansion ,DNode  Status as  Offline  How to investigate ？

• How to smoothly shrink a cluster ？

• Novice benefits ： Quick start  
  TDengine
    modeling .

1.  Why do I write data in batches , Timestamp use  NOW  Function splicing will result in data loss ？

To answer this question, we first need to emphasize a concept ,TDengine  As a

Time series database

（Time-Series Database）, The first timestamp field acts as a primary key , Construction of memory index 、 The storage of disk data is closely related to it , There must be no duplicate timestamp .

NOW  function （ as well as  NOW  keyword ） Return the current time of the client . When performing batch writes , If the values given by the timestamp in the first column are  NOW, It is indistinguishable under the time level of milliseconds by default in the database , Repeated timestamps written later will be lost or updated , The specific logic for handling repeated timestamps is provided in  TDengine  China Construction Library （Database） At the time of the  Update  Parameter determination .

2.  How to smoothly expand the capacity of a cluster ？

To expand the cluster, you need to add nodes manually . The specific operation steps are as follows ：

• After the first node is successfully deployed , Install nodes to be added in sequence  TDengine  Server program , edit  /etc/hosts, Add the domain name resolution of all nodes in the cluster （ If deployed  DNS server, There is no need to edit ）.

• The configuration file of the first node  taos.cfg  Copy to the node to be added , Will be one of the  fqdn  The parameter is changed to the node itself  fqdn (hostname).

• Start the node to be added  taosd  service , Then enter  taos  The command line executes the following statement to add the node to be added into the cluster ：CREATE DNode ‘Node2:6030’ .

• perform  SHOW DNodes  Check whether the status of the data node is  Ready. by  Ready  On behalf of successful cluster expansion .

3.  After cluster expansion ,DNode  Status as  Offline  How to investigate ？

After the new node joins the cluster normally , The data node list will show that the node is in  Ready  state . If the node status is  Offline, Check according to the following contents ：

• View the node  taosd  Started or not 、 Whether the firewall is closed ;

• Confirm whether the data folder of the node to be added is empty ;

• Check all nodes  /etc/hosts  Whether the domain name resolution is complete 、 It works （ All nodes need to be resolved , Include  arbitrator）;

• The node  firstEP、fqdn  Whether the parameters are configured correctly .

4.  How to smoothly shrink a cluster ？

Cluster capacity reduction is achieved through  DROP DNode  Delete nodes to achieve , Stop specifying directly  DNode  Of  taosd  The process will only let this node  Offline, But it cannot complete the effect of volume reduction . The specific operation steps are as follows ：

• Get into  taos  Command line , perform  SHOW DNodes  Check the status of the node to be deleted , if  ready  Then proceed to the next step ;

• Delete the specified node from the current cluster  DROP DNode ‘Node2:6030’  perhaps  DROP DNode <DNodeId>.

• perform  SHOW DNodes  View the cluster node information , Finally, confirm that the information of the node to be deleted has disappeared from the list .

Be careful ： Before deleting nodes , The cluster will  DNode  Data is migrated to other nodes , The completion speed depends on the bandwidth of the network 、 On disk  IO, Never stop the node to be deleted before it is completed  taosd  service .

5.  Novice benefits ： Quick start  TDengine  modeling .

In the process of community support , You can find many novice partners deploying  TDengine  I don't know how to further experience , Our suggestion is to run the sentences in the official website documents , But there are many documents , In order to facilitate community partners to get started quickly , We condense the example model of the official website document 、 I summed it up , Let users know as soon as possible  TDengine  Modeling methods ：

[ Introduction to modeling ]

complimentary close

Thank you for reading the selected questions in this issue , I hope the above is helpful to you . You are using  TDengine  This kind of  TIme-Series Database  In the process of , If you encounter a difficult problem or have a problem with  TDengine  There are suggestions for improvement , Welcome to the &nbsp;

GitHub

&nbsp; Let's talk about  Issue , The more detailed the content, the better , You can also scan the QR code below wechat to join the community , Communicate with you  ~  Last , Thank you for using  TDengine！

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TDengine Database

Specific details of , Welcome to

GitHub

View the relevant source code on .